The starburst effect available for weapon fire and used on the QAC in vanilla has a hit-detection area much larger than the actual graphical effect. I think the engine is trying to make it so that any hit within the radius of the spikes is counted, but it's getting it very wrong....my small-scale testing indicates that on the stock QAC a stray rock travelling anywhere near the shot will register a hit. This, combined with the absurdly low HP results in it being extremely easy to shoot down. This problem also carries over to modded weapons, and makes them disproportionately vulnerable to being shot down. On the other hand, it also means they can soak up an absurd amount of enemy fire....currently the QAC is useless as an actual weapon, but makes a surprisingly good point-defense system against beam-spam enemies.

To test: Equip QAC, a NAMI missile launcher, and a hold full of KM120s. Find an asteroid belt. Fire a KM120 at a rock, turn to one side slightly and immediately fire the QAC, then pause the game and advance it by single frames. The effect is very apparent if you get the timing right.

Edit: Sub-suggestion.....while testing this, it's also really apparent just how bad the default hit graphics are....you can clearly see that they're getting cut off into squares (same problem with Luminous based graphics that plagues a lot of explosions). It's probably on the list for a redo at some point (I can't access Ministry at present so I can't check the tracker), but if it isn't it really should be.